The conventional tractor-trailer hitch or coupling structure has been standardized so that practically any tractor or fifth-wheel truck can be coupled to any trailer. Truck trailers and recreational fifth-wheel trailers have a kingbolt or kingpin depending from the forward end that is engaged and pulled by a tractor or truck with a fifth wheel. A fifth-wheel has a skid plate with an opening in which the pin is engaged and carried. The kingpin has an annular groove that is engaged by movable jaws of the fifth wheel. When the kingpin is locked into engagement with the fifth wheel, the trailer can be hauled by the tractor or truck.
Often, when a semi-trailer is delivered to its destination, it is uncoupled from the tractor and left until it is unloaded, reloaded or stored. Similarly, recreational fifth-wheel trailers are often left unattended when it is desired to store them and use the hauling vehicles for personal transportation. Thus, trailers are often left unattended. Because of the standardization of fifth-wheel hitches, it is simple for a thief to couple his or her own tractor or truck to an unattended trailer and haul it away.
In order to deter such occurrences, various devices have been developed to enclose the kingpin in a portable housing to prevent the attached trailer from being stolen. For instance, Johnson et al. in U.S. Pat. No. 3,600,914 disclose a lock body having a hemispherical surface. It requires a set screw in a bore to engage the groove of the kingpin. A removable lock cylinder then is inserted into the bore and a cam element locked into a side groove to prevent access to the set screw. While effective, this device requires a massive body and the manipulation of a set screw as well as a lock cylinder. It thus tends to be awkward to install and remove and somewhat expensive to manufacture.
An even more complex, and therefor expensive apparatus is disclosed by Kayser in U.S. Pat. No. 3,757,550. This device includes a housing that fits over the kingpin and an axially extending lock cylinder, mounted on the housing, that moves a plurality of pivoting members into engagement with the kingpin groove.
A more simplified approach is shown in U.S. Pat. No. 4,620,718 issued to Mickelson. A housing for enclosing the kingpin has an enlarged portion extending from a cavity that receives the kingpin. This enlargement has a channel into which a sliding member is inserted until an end extends into the kingpin groove. The sliding member has a lateral slot corresponding to a slot in the enlarged housing portion for receipt of the body of a padlock. The padlock secures the sliding member. This apparatus is also effective, but is very heavy if made of a durable metal capable of withstanding physical tampering.
A substantially lighter device is described by Dykes in U.S. Pat. No. 4,704,883. This device simply includes a housing for enclosing the kingpin. A lock cylinder extends through a laterally extending tube for selective engagement of the kingpin groove by a cam element. This device is subject to possible physical removal by hammering on the protruding lock cylinder until it breaks or overpowering the lock cam element by prying on the housing.
Another device which is clever but also subject to being defeated by physical attack is that disclosed in U.S. Pat. No. 4,841,756 issued to Curtis. This device also has a housing for enclosing the kingpin. It is similar to the device of Mickelson but without the slider element. Curtis' device simply uses the lock shackle to engage the groove of a kingpin. Although favorable for its simplicity, the only thing securing the device on the kingpin is the shackle. It is likely that with sufficient weight, the shackle could be overcome and the device removed by sufficient prying on the housing.
There thus remains a need for a kingpin locking apparatus that is simple in structure, and therefor relatively inexpensive to make, while being sturdy enough to withstand substantial physical attack.